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Volume 80, Issue 11
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KEIJI WADA1985 Volume 80 Issue 11 Pages 467-483
Published: November 05, 1985
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSCalc-alkalic andesites from the Funagata volcano are characterized by disequilibrium phase assemblages, reverse zoning of plagioclase and pyroxenes, wide compositional range of plagioclase, and coexistence of basaltic and rhyolitic glass inclusions. These mineralogical features can be ascribed to magma mixing process involved in the formation of the calc-alkalic andesites. Compositional profiles of plagioclase and pyroxenes suggest that the phenocrysts have crystallized from three distinct magmas such as mafic and silicic end-member magmas and mixed magma. Mixing ratio of mafic end-member magma to silicic end-member magma within individual andesite was calculated by available mineralogical data. Whole-rock chemical composition of andesites exhibits linear correlation with both the mixing ratio and SiO2 content. Two mixing lines in MgO-K2O diagram are constricted at the MgO-rich tholeiitic basalts which represent the mafic end-member magma. Chemical composition of the silicic end-member magmas was deduced by the mixing ratio. Calculated two silicic end-members are felsic andesite (SiO2=64%, K2O=1.1%) and dacite (SiO2=66%, K2O=1.8%). Available Sr-isotopic data suggest that the dacite magma is not produced by fractional crystallization of the tholeiitic magmas.View full abstractDownload PDF (1031K) -
Part 2 Chemical propertiesShinobu Tanaka, Takahiko Maruyama1985 Volume 80 Issue 11 Pages 484-498
Published: November 05, 1985
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe Funatsu granitic complex in the Hida Mountains intruded into the metamorphic rocks of the Hida Metamorphic Belt and Hida Marginal Belt. This complex consists of three granitic rock types; Shimonomoto, Nakasawa and Funatsu types in the order of emplacement (Tanaka and Maruyama, 1985). As many samples were collected from these rock types, 6 specimens were analysed by ion-exchange resins and chelate-titration methods, and 30 specimens by X-ray fluoresence spectrometric (XRF) method on major elements. 110 specimens were analysed by XRF method on some minor elements.
Slightly different trends among these three types are shown in the variation diagram of major elements against SiO2 (Fig. 1), and larger differences are found among minor elements of Ba, Rb and Sr in whole rock (Fig. 2). The Shimonomto and Funatsu types among three types are plotted in the different fields and have independent differentiation trends on (Fe2O3+FeO)-MgO-(Na2O+K2O) diagram (Fig. 4), on normative Or-Ab-An diagram (Fig. 5), on Rb-Ba-Sr diagram (Fig. 6) and on Sr-Rb/Sr diagram (Fig. 7). These chemical characters suggest that both types might be derived from different magma. Furthermore, solidifing depth of each magma is considered to have been different by normative SiO2-Or-Ab system (Fig. 3).
The discordant result of the Rb-Sr whole-rock age in this complex between Tanaka et al. (1983) and Shibata and Nozawa (1984) may be attributed to the difference in rock-type classification, to the degree of alteration effect, and to some differences in sampling localities. It may be pointed out that the evaluation of the age data of the Shimonomto type is 208.6 Ma or older, and that for the Funatsu type is 180.9 Ma.View full abstractDownload PDF (895K) -
HARUO OHASHI, TOSHIKAZU OSAWA, KATSUHIRO TSUKIMURA1985 Volume 80 Issue 11 Pages 499-502
Published: November 05, 1985
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe crystal structure of Cd3Al2Si3O12 garnet grown by the solid state reaction method has been refined by the least squares method using 316 reflections measured with an automatic single crystal diffractometer. The unweighted R factor is 0.039 for 244 observed reflections. The cell dimensions are: a=11.805Å, and V=1645.26Å3; space group Ia3d. The Si-O distance is 1.644 (5)Å.
Comparison of the Si-O distance in the Cd3Al2Si3O12 garnet with those in six M2+3Al2Si3O12 garnets, previously published, indicates that the electronegativity of Cd2+ ion in the dodecahedral site of the garnet is about 1.3 in Pauling's scale. This value is more electropositive than the thermochemical electronegativity value (1.5). Since the ionicity of the chemical bonding increases with an increase in the coordination number, it seems that the electronegativity of Cd2+ ion decreases with an increase in the ionicity of the chemical bonding.View full abstractDownload PDF (268K) -
MICHIO TAGIRI1985 Volume 80 Issue 11 Pages 503-506
Published: November 05, 1985
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSA map of the graphitizing-degree has been drawn for the Sanbagawa metamorphic belt of central Shikoku, and compared with the metamorphic zones previously reported. The distribution of the graphitizing-degree (GD) is very consistent with the mineral zones of this district, showing minute thermal structures in the metamorphic zones, and suggests the extension of the oligoclase-biotite zone to the areas of the Tachikawa River and the Saruta River. The local disturbance of GD seems to be due to a tectonic event affecting rocks of the lower (or higher) metamorphic grade.View full abstractDownload PDF (230K) -
ALBERTO C. SÁNCHEZ, KATSUTOSHI TANIDA, TSUYOSHI KITAMURA1985 Volume 80 Issue 11 Pages 507-510
Published: November 05, 1985
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSChemical, physical, optical, X-ray and thermal data for dickite from San Pablo mine, La Paz Department, Boliva are given. The occurrence of dickite in Bolivia are recorded from some Potosi type mine in the Potosi and Oruro districts. However, the mineralogical data have not published.View full abstractDownload PDF (814K)
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